1. Field of the Invention
The present invention relates to a drive device and an image forming apparatus that use a grease composition, and the grease composition used for the drive device and the image forming apparatus.
2. Description of the Related Art
Image forming apparatuses employing an electrophotographic process use many drive devices in mechanisms for an image reading process, an image forming process, a transfer process, and a paper conveyance process, for example. Conventional image forming apparatuses are large-sized and handled as precision apparatuses. The image forming apparatuses are, thus, often installed in places apart from people who perform office operations in offices such as dedicated rooms provide for the apparatuses. Sounds generated during the process for forming images by such image forming apparatuses, thus, are not a serious problem. In fact, the start of forming an image is checked by the generated sound and the end of forming the image is recognized by the stop of the sound.
With the progress of downsizing of the image forming apparatuses in recent years, cases have been increased in which the image forming apparatuses are installed in places just near users such as on the user's desks or side desks. A plurality of users often access an image forming apparatus through a local area network (LAN) to instruct the image forming apparatus to form an image using user's personal computers. As a result, the operating rate of the image forming apparatus tends to be increased. Sounds generated by the image forming apparatuses, which have not been a serious problem, can be often hard to bear for the users near the place in which the image forming apparatuses are installed. In addition, offices are quiet these days. Sounds generated from the image forming apparatuses, thus, become more noticeable.
Most of the generation sources of sounds from the image forming apparatuses are the drive devices described above. The drive devices drive objects by transmitting kinetic energy from the driving sources such as motors to the objects through gears and belts, for example. The image forming apparatuses each include many drive devices. In particular, the gears are very important parts for the transmission of the kinetic energy of the driving sources. Such a drive device is usually provided with many gears. A sound is generated from the drive device due to rubbing between tooth flanks of engaged gears, rubbing between a slide bearing and a shaft to which a gear is fixed, and rubbing between a shaft fixed non-rotatably and the gear rotating on the shaft, for example.
As examples the image forming apparatuses that reduce a noise generated by rubbing between the tooth flanks of the gears, image forming apparatuses in Japanese Patent Application Laid-open No. 2010-083658 and Japanese Patent Application Laid-open No. 2003-312868 have been developed that reduce a noise by a grease composition applied on the tooth flanks of the gears. In Japanese Patent Application Laid-open No. 2001-228660, a drive device is disclosed that uses gears having grooves to hold a grease composition for preventing the grease composition from coming off from the tooth flanks. As examples such as the image forming apparatuses and the drive devices described above, conventionally, it has been common practice to apply a grease composition used for reducing a noise mainly on the tooth flanks of gears. It is considered that a slightly hard grease composition containing a solid lubricant such as polytetrafluoroethylene, molybdenum disulfide, graphite, or melamine cyanurate has a high effect of reducing a noise. Such a grease composition prevents a hitting sound from being generated by a direct contact between the gears, and reduces friction and wear between the gears, thereby making it possible to maintain the smooth rotation of the gears. The reason why a slightly hard grease composition, specifically, a grease composition having a low consistency, is used is that an excessively soft grease composition may come off from the tooth flanks by a centrifugal force during the operation of the drive device. Conventionally, it has been considered that a noise from the drive device is mainly generated from the tooth flanks of gears and a noise generated between a shaft and a gear rotating on a peripheral surface of the shaft passing through a hole of the gear is not considerable.